思归等大人帮忙一下，怎么在winform中模拟一个webform的表单提交，其中这个表单是上传文件的 encType=multipart/form-data

如题 ，没有文件上传的可以作到 ，encType=multipart/form-data为中该这么写：

下面是没有文件上传的普通表单提交！

Public Function PostDate(ByVal url As String, ByVal PostData() As String) As String
Dim Post As String = ""
For Each s As String In PostData
Post += s + "&"
Next
Post = Post.Substring(0, Post.Length - 1)
Dim html As String = ""

Dim encoding As Encoding = encoding.GetEncoding("GB2312")
Dim data As Byte() = encoding.GetBytes(Post)
Dim myRequest As HttpWebRequest = CType(WebRequest.Create(url), HttpWebRequest)
myRequest.Method = "POST"
myRequest.ContentType = "application/x-www-form-urlencoded"


myRequest.ContentLength = data.Length
Dim newStream As Stream = myRequest.GetRequestStream()
newStream.Write(data, 0, data.Length)
newStream.Close()
Dim resp As HttpWebResponse = CType(myRequest.GetResponse(), HttpWebResponse)
Dim sr As StreamReader = New StreamReader(resp.GetResponseStream(), System.Text.Encoding.Default)
html = sr.ReadToEnd()

Return html
End Function


使用：
Dim postdata As String() = {"id=luajiu", "pw=xxxx", "ipmask=0"}

Dim strUrl As String = "http://bbs.cau.edu.cn/wusetu.cn/bbslogin"


Dim SessionHtml As String = PostDate(strUrl, postdata)


有文件上传的该怎么改啊！